Rulings by Egypt's Supreme Constitutional Court are a blow to the Muslim Brotherhood and strengthen the military's hand.

CAIRO — The battle between Egypt's military leaders and the ascendant Muslim Brotherhood over the country's political fate dramatically sharpened when the nation's constitutional court dissolved the Islamist-dominated parliament while upholding the right of an ally of deposed leader Hosni Mubarak to remain on this weekend's presidential election ballot.

The decisions by the Supreme Constitutional Court on Thursday strengthened the army's hand and tipped the nation into disarray two days before the presidential runoff begins. They are a setback for the Brotherhood, which controlled nearly half of parliament and expected to expand its power if its candidate, Mohamed Morsi, defeated Ahmed Shafik, the last prime minister to serve Mubarak, in voting that concludes Sunday.

The court rulings strike at the core of Egypt's long, often bloody struggle over what ideology will govern the Arab world's most populous nation. After enduring years of persecution and arrests, the Brotherhood, the country's most potent opposition under Mubarak, rose to prominence and closed in on its goal of imposing political Islam with its strong showing in May's first round of voting. But the nation's interim rulers — many of them army generals appointed by Mubarak — appear loath to bow to a new era that could compromise their authority.

Activists characterized the rulings as a maneuver by the military to weaken the Brotherhood ahead of the army's promise to hand power to a civilian government by July. Some fear that a victory by Shafik, a retired air force general, would cement the military's grip and upend the demands for democratic change that fueled the uprising last year that brought down Mubarak, Egypt's autocratic leader for three decades.

"All this equals a complete coup d'etat through which the military council is writing off the most noble stage in the nation's history," Mohamed Beltagy, a member of parliament with the Brotherhood's Freedom and Justice Party, said on his Facebook page. "This is the Egypt which Shafik and the military council desire."

It's not clear what effect the rulings will have on the presidential election and the struggle to draft a constitution. Activist groups have grudgingly announced their backing of Morsi in recent days, support that could grow in the wake of the court decisions. The Brotherhood did not say exactly how it would respond to the rulings, a signal that perhaps Morsi and the army may have reached a power-sharing deal.

"We believe it's a political situation, not a constitutional one," Dina Zakaria, co-founder of the group's Foreign Relations Committee, told the Ahram Online news website. "The counterrevolution is trying to revive the old regime and will not accept civilian rule."

The army's hold on the country has increased in recent months while support for the Brotherhood has slackened. Many Egyptians, rich and poor, have been anxious over ongoing unrest and have looked to the generals and Shafik to stem crime and economic downturn. Despite Morsi's making it to the runoff election, the Brotherhood's image has been damaged by its broken political promises — including a vow that it would not field a presidential candidate — and suggestions that it is more politically opportunistic than committed to fulfilling the ideals of the revolution.

This could dampen turnout for anti-military protests planned for Friday.

Shafik, prime minister during the bloodiest days of last year's rebellion, has the military, state institutions and old guard businessmen behind him. Such backing without an elected legislative balance could, if he wins, lead to despotic rule, say activists, including Mohamed ElBaradei, a Nobel Peace Prize laureate.

"The election of a president in the absence of a constitution and a parliament is the election of a president with powers that not even the most entrenched dictatorships have known," ElBaradei said.

The court's decision on Shafik was not surprising. The judges were appointed by Mubarak and the law passed by parliament to prohibit former top government officials from running for president was widely regarded as unconstitutional. The law was supported by activists and the Brotherhood as a last chance to keep remnants of the old guard at bay and revive a revolution that inspired the Arab world.

Without a sitting parliament, the new president will be likely to influence the drafting of a constitution and legislative elections. That is almost certainly true if Shafik wins but less so if Morsi does. It's not clear how and when new elections would occur. That will be determined by Field Marshal Mohamed Hussein Tantawi, leader of the military council.

Shafik termed the rulings a vindication: "The age of settling accounts is over and gone," he said at a news conference. "The age of using the law and the country's institutions against any individual is over."